Japan's Emperor Akihito has expressed concern about fulfilling his duties as he ages, and hinted that he may want to abdicate in a few years.

His comments came in a rare address to the public on Monday.

"When I consider my age of over 80, as well as my gradually deteriorating physical condition despite being luckily healthy at this moment, I am concerned about being able to fulfil my duties as a symbol with the utmost efforts, as I have done so far," Akihito said in a 10-minute recorded speech which was broadcast on national television.

Japan's post-Second World War constitution restricts what the emperor can say as a symbolic monarch with no political power. As expected, Akihito avoided explicit mention of abdication, which could have violated those restrictions.

Responding to his message, Prime Minister Shinzo Abe said he takes seriously what Akihito said.

"I think we have to thoroughly think what we can do to accommodate his concerns, taking into consideration the emperor's age and the current burden of official duties," Mr Abe said.

The 82-year-old monarch spoke publicly after recent media reports that he may want to abdicate because he did not want to cling to the title if his duties had to be severely reduced.

Abdication is not allowed under the current imperial law, largely inherited from the pre-war Constitution which banned the practice as a potential risk to political stability.

Media reports said the government may consider a special law for one-time abdication just for Akihito as an exception.

Akihito suggested in his speech a need to consider how to make the succession process smoother.

His two sons have reportedly accepted the idea of an abdication. His elder son, Crown Prince Naruhito, is the likely successor.